Read the entire article at https://www.macrumors.com/how-to/night-shift-macos-sierra-10-12-4/
For those unfamiliar with Night Shift, it’s designed to cut down on the amount of blue light you’re exposed to during the evening by shifting the display of a Mac to a more yellow tone. Blue light is said to have a harmful effect on your circadian rhythm, making it harder to fall asleep and stay asleep.
Studies suggest that eliminating blue light exposure at night might help you sleep just a bit better, but it does significantly change the look of your display. Many Mac users have been using blue light reduction software f.lux for years now, but with Night Shift, there’s no need to install an additional app because it’s an operating system feature.
Turning On Night Shift :